The invention relates to a data processing device. A data processing device is described in the architectural overview of the Philips 80C51XA processor, published in the "1996 Data handbook" IC25 published by Philips Semiconductors, pages 33 to 56.
It is desirable to minimize the amount of memory space needed for storing the instructions from a program for such a processing device. A reduction of the amount of memory space can be realized by using an instruction set with instructions of various lengths, e.g. 8, 16 or 24 bits, the most frequently occurring instructions being coded with the shortest length.